Antioxidant and cytotoxic activities of quinones from Cetraria laevigata .

Chemical investigation of the extracts obtained from the red thallus tips from Cetraria laevigata resulted in the isolation of five known quinoid pigments identified by FT-IR, UV, NMR, MS methods and by comparison with literature data (skyrin ( 1 ), 3-ethyl-2,7-dihydroxynaphthazarin ( 2 ), graciliformin ( 3 ), cuculoquinone ( 4 ) and islandoquinone ( 5 )). An antioxidant capacity of compounds 1 - 5 were evaluated and compared with quercetin using a lipid peroxidation inhibitory assay and superoxide radical (SOR), nitric oxide radical (NOR), 1,1-diphenyl-2-picrylhydrazine (DPPH), 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) scavenging assays. Compounds 2, 4 and 5 were far more active: they demonstrated the antioxidant capacity in various test assays with the IC 50 values 5-409 µM comparable to the flavonoid quercetin. While, the isolated quinones ( 1-5 ) exhibited weak cytotoxicity in human cancer cell line A549 assessed by MTT assay.